Require Znumtheory before using it

For rocq-prover/stdlib#136

Author: andres-erbsen

lib/IEEE754_extra.v

@@ -23,6 +23,7 @@ Require Import SpecFloat.
 From Flocq Require Import Core Digits Operations Round Bracket Sterbenz
                           BinarySingleNaN Binary Round_odd.
 Require Import ZArith.
+Require Znumtheory.
 Require Import Psatz.
 Require Import Bool.
 Require Import Eqdep_dec.